Sportomatic gearbox - Porsche’s first automatic gearbox is more than half a century old… here’s how it works
Introduced to the world in 1967 by Porsche, the Sportomatic was the company’s answer to reinvigorating the 911 range for a push in the USA, where automatics were gaining huge popularity. At its heart is an all-synchro, four-speed 901 manual, but with a torque convertor and single dry-plate clutch.
Technology explained - SPORTOMATIC GEARBOX
That clutch is controlled by a microswitch on the gear lever. Move the gear lever and the microswitch activates a vacuum servo motor. This then moves a lever, disengaging the clutch – which is the automatic element here. When the gear lever stops moving as the next gear is selected, the microswitch then enables the clutch to be reengaged, and drive is taken back up.
Two pedals in a Porsche 911, first seen in 1967
The system permits little clutch slip, allowing a smaller single-plate clutch to be utilised; a useful benefit for weight saving. Crank rotation is transferred to the clutch via a torque convertor, using engine oil fed by a pump driven by the engine’s camshaft, pumping fluid from the engine’s own supply – although it needs 2.37 litres on top of the engine’s capacity. With this arrangement, gears could be selected and changed at will – in under half a second, it was claimed. Stopping the 911 required only the brake, with no need to either take the car out of gear or manually disengage drive. The design brought many benefits, not least because of the high stall speed of the torque convertor, which meant any gear could be used to move from a standstill.
The gearbox stayed in production until 1979, with an update in 1975 to cope with the extra potency of the 2.7 engine. Those later Sportomatics used the 915 gearbox as a base and had three, rather than four speeds.
Thanks to its ostensibly manual operation, the Sportomatic gearbox wasn’t the first automatic transmission to feature in a 911. That honour falls to Tiptronic.
The Sportomatic then, is typically Porsche. Forward thinking, robustly engineered – they’re capable of huge mileages without issue – and proven in racing, thanks to Vic Elford in 1967 driving a Sportomatic-equipped 911R to victory in the 84-hour Marathon de la Route at the Nürburgring. Yet despite these accolades the option never really took off with buyers, not least perhaps because the market demands sports cars have manual ‘boxes. Something Ferry Porsche himself was aware of at the time.
The modern PDK may be the epitome of what an automatic gearbox should be in a 911, but we owe a debt to the Sportomatic, its overlooked predecessor.